arXiv subjects

Kojiro Tanaka

Publications and source records attributed to Kojiro Tanaka.

5 recordsLinked to original sources

arXiv2026

Narrow iron- and nickel-K absorption lines from the eclipsing low-mass X-ray binary AX~J1745.6$-$2901

We report the presence of a highly ionized absorber in the transient, eclipsing low-mass X-ray binary AX J1745.6-2901, observed from Feb. 26 to 29, 2024 with XRISM's Resolve and Xtend instruments. During a soft/high state without dips, Resolve's high spectral resolution (E/dE ~ 1000, full width at half maximum) revealed narrow velocity widths (sigma ~ 110 km/s) for Fe XXVI and Ni XXVIII lines, even with low photon statistics. These widths are consistent with binary orbital motion. The observed modest blueshift velocity (~160 km/s) indicates that the absorber is located sufficiently far from the neutron star (> 10^9 cm), so that gravitational redshift effects are not dominant. On the other hand, broad-band spectral analysis using a photoionized plasma model applied to the Xtend data constrains the absorber to lie within a radius of < 10^9.5 cm, as inferred from the upper limits of the best-fit ionization parameter (log xi ~ 4.4) and the large column density (~ 1.6 x 10^24 cm^-2). At this distance, the observed outward velocity of the absorber is about an order of magnitude smaller than the escape velocity from the neutron star.

astro-ph.HE↗

arXiv2025

XL-Calibur measurements of polarised hard X-ray emission from the Crab

We report measurements of the linear polarisation degree (PD) and angle (PA) for hard X-ray emission from the Crab pulsar and wind nebula. Measurements were made with the XL-Calibur ($\sim$15-80 keV) balloon-borne Compton-scattering polarimeter in July 2024. The polarisation parameters are determined using a Bayesian analysis of Stokes parameters obtained from X-ray scattering angles. Well-constrained ($\sim$8.5$σ$) results are obtained for the polarisation of the $\sim$19-64 keV signal integrated over all pulsar phases: PD=(25.1$\pm$2.9)% and PA=(129.8$\pm$3.2)$^\circ$. In the off-pulse (nebula-dominated) phase range, the PD is constrained at $\sim$4.5$σ$ and is compatible with the phase-integrated result. The PA of the nebular hard X-ray emission aligns with that measured by IXPE in the 2-8 keV band for the toroidal inner region of the pulsar wind nebula, where the hard X-rays predominantly originate. For the main pulsar peak, PD=(32.8$^{+18.2}_{-28.5}$)% and PA=(156.0 $\pm$ 21.7)$^\circ$, while for the second peak (inter-pulse), PD=(0.0$^{+33.6}_{-0.0}$)% and PA=(154.5 $\pm$ 34.5)$^\circ$. A low level of polarisation in the pulsar peaks likely does not favour emission originating from the inner regions of the pulsar magnetosphere. Discriminating between Crab pulsar emission models will require deeper observations, e.g. with a satellite-borne hard X-ray polarimeter.

astro-ph.HE↗

arXiv2025

Exploring Interactive Simulation of Grass Display Color Characteristic Based on Real-World Conditions

Recent research has focused on incorporating media into living environments via color-controlled materials and image display. In particular, grass-based displays have drawn attention as landscape-friendly interactive interfaces. To develop the grass display, it is important to obtain the grass color change characteristics that depend on the real environment. However, conventional methods require experiments on actual equipment every time the lighting or viewpoint changes, which is time-consuming and costly. Although research has begun on simulating grass colors, this approach still faces significant issues as it takes many hours for a single measurement. In this paper, we explore an interactive simulation of a grass display color change characteristic based on real-world conditions in a virtual environment. We evaluated our method's accuracy by simulating grass color characteristics across multiple viewpoints and environments, and then compared the results against prior work. The results indicated that our method tended to simulate the grass color characteristics similar to the actual characteristics and showed the potential to do so more quickly and with comparable accuracy to the previous study.

cs.GR↗

arXiv2024

ProgrammableGrass: A Shape-Changing Artificial Grass Display Adapted for Dynamic and Interactive Display Features

There are various proposals for employing grass materials as a green landscape-friendly display. However, it is difficult for current techniques to display smooth animations using 8-bit images and to adjust display resolution, similar to conventional displays. We present ProgrammableGrass, an artificial grass display with scalable resolution, capable of swiftly controlling grass color at 8-bit levels. This grass display can control grass colors linearly at the 8-bit level, similar to an LCD display, and can also display not only 8-bit-based images but also videos. This display enables pixel-by-pixel color transitions from yellow to green using fixed-length yellow and adjustable-length green grass. We designed a grass module that can be connected to other modules. Utilizing a proportional derivative control, the grass colors are manipulated to display animations at approximately 10 [fps]. Since the relationship between grass lengths and colors is nonlinear, we developed a calibration system for ProgrammableGrass. We revealed that this calibration system allows ProgrammableGrass to linearly control grass colors at 8-bit levels through experiments under multiple conditions. Lastly, we demonstrate ProgrammableGrass to show smooth animations with 8-bit grayscale images. Moreover, we show several application examples to illustrate the potential of ProgrammableGrass. With the advancement of this technology, users will be able to treat grass as a green-based interactive display device.

cs.GR↗

arXiv2022

Dynamic Grass Color Scale Display Technique Based on Grass Length for Green Landscape-Friendly Animation Display

Recently, public displays such as liquid crystal displays (LCDs) are often used in urban green spaces, however, the display devices can spoil green landscape of urban green spaces because they look like artificial materials. We previously proposed a green landscape-friendly grass animation display method by controlling a pixel-by-pixel grass color dynamically. The grass color can be changed by moving a green grass length in yellow grass, and the grass animation display can play simple animations using grayscale images. In the previous research, the color scale was mapped to the green grass length subjectively, however, this method has not achieved displaying the grass colors corresponding to the color scale based on objective evaluations. Here, we introduce a dynamic grass color scale display technique based on a grass length. In this paper, we developed a grass color scale setting procedure to map the grass length to the color scale with five levels through image processing. Through the outdoor experiment of the grass color scale setting procedure, the color scale can correspond to the green grass length based on a viewpoint. After the experiments, we demonstrated a grass animation display to show the animations with the color scale using the experiment results.

cs.GR↗